1. Field of the Invention
The invention relates to electrophotographic copiers and, more particularly, to document handling in electrophotographic copiers permitting stacks of originals to be automatically copied a desired number of times.
2. Description of the Prior Art
There are essentially two ways of copying original documents and placing the copies in a desired order when more than one original is the source of copies. A collator may be provided to place copies into bins in sequence determined by the number of originals. In this case, each original is held for copying the desired number of copies and then the next original is chosen. Collators require significant amounts of physical room and are mechanically complex. An alternative approach is to make one copy from each original, thus stacking the copies in the same sequence as the originals, and then recirculate the originals for further copying. This gives a single stack of correctly-sequenced copies, but has the disadvantage of causing additional handling of the original. Automatic recirculation, in the prior art, is obtained by removing original sheets from a stack bottom, placing them on a document platen, exposing the document for purposes of copying and then returning the original to the top of the stack. This operation involves at least two significant shortcomings.
First, removal of sheets from the bottom of a stack introduces the possibility of damage to the original because the force bearing on the bottom of the stack is subject to many variables such as the number of originals provided. Second, the speed of operation is dependent upon the speed at which the original can be exposed as well as the speed at which it can be removed and returned to the stack. Therefore, due to the long mechanical path involved, this technique is often limited to "flash exposure" of the original as opposed to scanning the original with a bar of light. In instances where the latter approach is desirable, the described approach is not practical.
In U.S. Pat. No. 4,099,150 by John Lyman Connin, assigned to Eastman Kodak Company, and filed June 1, 1976, there is disclosed an apparatus for producing duplex copies in an automatic recirculating document feed copier. Originals are removed from the top of a stack in a first tray and fed to a second stack from which they are removed, bottom first, for copying. They are then returned after use to the top of the first stack for reuse. This approach has the disadvantage of reconstructing the upper tray in reverse order and retains the problem of removing sheets from the bottom of a stack.